1. Field of the Invention
The present invention relates to an improvement in a stator of a dynamo-electric machine which is assembled by sequentially inserting premolded coil pieces into a stator core.
2. Description of the Related Art
In general, a stator of a dynamo-electric machine has a stator core 10 which is, as shown in FIG. 7, constituted by stacking a plurality of annular metal plates each having slots 10a and teeth 10b (a portion interposed between two teeth is called a "slot") alternately formed along the inner periphery thereof. The stator further has coils 12, each of which is formed by continuously winding a coil wire coated with enamel or the like around the tooth 10b of the stator core 10. The stator shown in FIG. 7 is formed by a winding method which is so-called concentrated winding. In this method, one coil 12 is provided for one tooth 10b. One or a plurality of bundled wires each having a diameter ranging from about 0.5 mm to about 1.0 mm are wound around a tooth 10b a predetermined number of times. Therefore, the slot 10a is designed to receive adjacent ends of two coils fitted to two teeth 10b interposing the slot 10a. When an electric current is allowed to pass through each coil 12, a magnetic flux is generated in a direction along which the magnetic flux penetrates the coil 12 through the teeth 10b serving as a magnetic path. As a result, a rotor (not shown) can be rotated. The dynamo-electric machine acts as a dynamo-electric generator by rotating the rotor with the aid of an external force.
Generally it takes a long time to wind the coil wire around each tooth 10b as described above. Additionally it is difficult to automate such winding operation. Japanese Utility-Model Publication No. 2524074 discloses a structure arranged such that coil pieces, which have been molded to have a predetermined shape using a mold or the like, are fitted with the teeth 10b. In this case, the slots 10a accommodate the coil pieces, each of which is formed by winding a coil wire predetermined number of times across the teeth 10b. Therefore, the operation for assembling the stator can easily be completed. Moreover, the operation for winding the coil wire can easily be automated.
When the slots 10a for accommodating the coil pieces are formed along the inner periphery of the stator core 10 as shown in FIG. 7, the width of the open portion (the upper portion) of each slot 10a is smaller than that of the bottom portion (the lower portion) of the slot 10a. That is, the slot 10a has a shape which is gradually widened toward the bottom portion thereof. Therefore, the cross sectional width of the coil piece which is inserted into the slot 10a must be equal to or smaller than the width of the open portion of the slot 10a so as to prevent interference with a leading end of the tooth 10b. As a result, there is undesirable space formed within the slot 10a after inserting the coil piece having the above described shape into the slot 10a. Thus, the required space factor in the slot 10a cannot be obtained, resulting in problems such as deteriorated performance of the dynamo-electric machine.
It might be considered feasible to form each of the teeth 10b into a trapezoidal shape so as to form the slot 10a into a rectangular shape, as shown in FIG. 8. In this case, the coil pieces 14 must be gradually widened so as to be fitted with the trapezoidal teeth 10b. However, the coil pieces 14, each of which is formed by winding the coil wire a plural number of times, are too rigid to be widened as described above. Thus, there arises a problem in that fitting operation while widening the coil pieces is very difficult.
Another method has been suggested which has the steps of fitting the coil pieces 14 with sectioned portions of the stator core 10, and combining the sectioned portions of the stator core 10 with one another by welding or the like. Using the above-mentioned method, however, may deteriorate rigidity of the stator itself and fail to keep the accuracy of the shape to a predetermined level or more. This may result in deterioration of the dynamo-electric machine.